This invention is in the field of data acquisition systems. More particularly, it is concerned with apparatus and methods for detecting analog signals at widely spaced locations, coding these signals and transmitting them as trains of single bit digital pulses over a single pair of conductors to a distant recording location.
Still more particularly it concerns a system in which a plurality of separate detectors produce analog signals which are amplified, added to a shifting function of controlled amplitude, axis-crossing-coded and transmitted by a two conductor cable to a distant recording unit.
While this invention is useful in the acquisition of any type of analog signals such as in the field of data collection, vibration analysis, sonar signaling, nuclear technology, and so on, it is most appropriately useful in the area of seismic prospecting and as a matter of convenience will be discussed in that application.
In the prior art of the seismic method it has been customary to use a large plurality of separate groups of geophones each connected by a two conductor cable which carry the geophone signals to a distant recording unit. Here each of the separate signals from each of the separate pairs of conductors is separately amplified, controlled, multiplexed and converted from analog to digital form for storage on a magnetic medium. As the number of geophones and separate recording channels has increased, in order to provide greater surface coverage, and to speed and improve the data collection, the cost and complexity of the amplifying system, etc. have become prohibitive.